Immunology: Adaptive Defenses
● Adaptive = unique (everyone encountered different antigens aka no one has exactly the
same) / must know what to attack
● Infected by antigen? Adaptive defenses increase
→ Overview
● System must be primed before it can take effect
○ Must know what to attack
○ If there’s nothing to attack adaptive immunity is suppressed in the body, only
when you get an antigen increase and take effect
● 1800 experiment
○ Inject bacteria into an animal
■ Took fluid before and after animals were affected
○ Found that: there was an increase in proteins inside plasma after infection that
weren’t there before (increase in antibodies against infection)
○ Took serum (not plasma - serum is plasma minus clotting proteins) containing
those antibodies and used them to protect other animals not previously exposed
■ Animals got sick when infected but weren’t as sick as the first series as
animals and healed faster
● Characteristics of adaptive response
○ Specific recognition of pathogens
■ Need to recognize what to attack
■ What they attack = pathogen (disease causing microorganism /type of
virus or bacteria aka antigen )
○ Response is systemic
■ Systematic = spreads all over the body (not localized)
○ Response has memory
■ mounts a stronger attack on repeated exposure/ same strain
○ Injecting lymphocytes also offers protection
■ Not only fluid/ antibodies that offer protection but also immune cells
→ Types of Immunity
1. Humoral
● Humor = type of fluid
● Antibodies are present inside plasma ⇒ plasma is a type of fluid
○ Aka if talking about antibodies making you better, we’re talking about
humoral immunity
a. Antibodies are made by lymphocytes (cells) present in body as ‘humor’
i. Just because they’re made by cells doesn’t mean it’s cellular immunity
ii. Lymphocyte releases antibody to fluid which in turn is causing you to get
better, not the cell directly
2. Cellular
, a. Lymphocytes themselves defend the body (lymphocytes attack antigens)
→ Antigens
● Antigen: substances provoking an immune response (ie. any foreign cell)
○ Cell doesn’t recognize it, try attack it (needs to know what to attack)
○ Needs a way to distinguish self (normal body cells) vs nonself (any foreign cell)
● Self recognition
** a way to determine self vs nonself ⇒ some of the proteins on cell surface are
used as recognition system
○ Major histocompatibility complex (MHC) class I proteins - mostly all cells have
class 1 proteins integrated on its surface
■ except RBCs (have ABO)
■ Except Macrophages (plasma membrane has no MHC class 1 - destroys
antigen with exocytosis aka APC cell)
● Antigen presenting cell
○ Can engulf antigen → break it up → when released
APC presents what’s left over from that antigen for
other cells to destroy
○ MHC class II proteins (on APC cells)
■ Don’t want to kill class II proteins because they engulf
** golden rule:
1. if an immune cell recognizes class 1 MHC it will leave it alone because it is an
ordinary body cell → test cells = MHC class 1 → sees cell infected with virus →
kills cell (because this will also kill antigen)
2. Immune cell comes up against class 2 MHC → infected with antigen, won’t kill
cell because it is an APC cell and already engulfing antigens (acting as an
immune cell / doing its job)
→ Humoral Immunity
● Antigenic
determinants:
specific regions the
antibodies bind to
○ Body has to
make antibodies for each of these antigenic determinants to be able to tag cell
for destruction
○ Antibody only tags for destruction, doesn’t destroy it
,T vs B lymphocytes → work differently
- Infected with antigen,body makes antibodies
- B cells make antibodies (upregulate/ clone themselves)
- If this is the first time seeing the antigen it’s called the primary response (72
hours - 3 days)
Clonal selection - steps
1. B cells clone themselves upon encountering an antigen (1st degree response, 3-6 days)
2. Resulting plasma cells secrete antibodies into plasma ( 2000 every second)
a. “Antibody producing factories” - release antibodies into plasma aka humoral
immunity
3. Clone cells not differentiating into plasma cells become memory cells
a. Memory cells can stay with you for 20-30 years
b. Knows what antigen looks like
4. Re-infection produces a 2nd degree response
a. More antibodies are made secondary response (see below)
→ B-Cell Cloning
→ Humoral Response :
# of antibodies made
, - IgM (1) /IgG (2)= types of antibodies
*First exposure: day ⅔ (so nothing happens during this time)
*# of antibodies start increasing (primary exposure = small # of antibodies being made)
*# of antibodies starts to decrease after primary response
* day 28, re-exposed to same antigen, in ⅔ days # of antibodies skyrockets
→ Antibody Structure
● Antibodies your body makes are examples of: Immunoglobulins (Ig) [makes different
types: IgM, IgG]
○ 4 polypeptides / chains of amino
acids [2 Heavy, 2 Light]
○ What’s holding it together:
disulphide bonds (2 molecules of
sulfur)
○ Antibody monomer, T or Y shaped
- 2 antigen binding sites (recognize
antigenic determinant)
○ C (constant region)
■ Sequence of amino acids all
the same
○ V (variable region)
■ Sequence of amino acid
chains changes near the ends
■ This is because when the body is infected with different antigens V
regions try to attach to the antigen so they must make the ends specific to
those antigens
Image: Simplest type of antibody (monomer - looks like y or t)
● 4 polypeptide chains
○ Short chain = “light”
○ Long chain = “heavy”
→ Antibody Classes (the different types of immunoglobulins)
● Classification is based on C region in heavy chain
● IgD (1), IgG (2), IgE (3), IgA (4), IgM (5)
● Adaptive = unique (everyone encountered different antigens aka no one has exactly the
same) / must know what to attack
● Infected by antigen? Adaptive defenses increase
→ Overview
● System must be primed before it can take effect
○ Must know what to attack
○ If there’s nothing to attack adaptive immunity is suppressed in the body, only
when you get an antigen increase and take effect
● 1800 experiment
○ Inject bacteria into an animal
■ Took fluid before and after animals were affected
○ Found that: there was an increase in proteins inside plasma after infection that
weren’t there before (increase in antibodies against infection)
○ Took serum (not plasma - serum is plasma minus clotting proteins) containing
those antibodies and used them to protect other animals not previously exposed
■ Animals got sick when infected but weren’t as sick as the first series as
animals and healed faster
● Characteristics of adaptive response
○ Specific recognition of pathogens
■ Need to recognize what to attack
■ What they attack = pathogen (disease causing microorganism /type of
virus or bacteria aka antigen )
○ Response is systemic
■ Systematic = spreads all over the body (not localized)
○ Response has memory
■ mounts a stronger attack on repeated exposure/ same strain
○ Injecting lymphocytes also offers protection
■ Not only fluid/ antibodies that offer protection but also immune cells
→ Types of Immunity
1. Humoral
● Humor = type of fluid
● Antibodies are present inside plasma ⇒ plasma is a type of fluid
○ Aka if talking about antibodies making you better, we’re talking about
humoral immunity
a. Antibodies are made by lymphocytes (cells) present in body as ‘humor’
i. Just because they’re made by cells doesn’t mean it’s cellular immunity
ii. Lymphocyte releases antibody to fluid which in turn is causing you to get
better, not the cell directly
2. Cellular
, a. Lymphocytes themselves defend the body (lymphocytes attack antigens)
→ Antigens
● Antigen: substances provoking an immune response (ie. any foreign cell)
○ Cell doesn’t recognize it, try attack it (needs to know what to attack)
○ Needs a way to distinguish self (normal body cells) vs nonself (any foreign cell)
● Self recognition
** a way to determine self vs nonself ⇒ some of the proteins on cell surface are
used as recognition system
○ Major histocompatibility complex (MHC) class I proteins - mostly all cells have
class 1 proteins integrated on its surface
■ except RBCs (have ABO)
■ Except Macrophages (plasma membrane has no MHC class 1 - destroys
antigen with exocytosis aka APC cell)
● Antigen presenting cell
○ Can engulf antigen → break it up → when released
APC presents what’s left over from that antigen for
other cells to destroy
○ MHC class II proteins (on APC cells)
■ Don’t want to kill class II proteins because they engulf
** golden rule:
1. if an immune cell recognizes class 1 MHC it will leave it alone because it is an
ordinary body cell → test cells = MHC class 1 → sees cell infected with virus →
kills cell (because this will also kill antigen)
2. Immune cell comes up against class 2 MHC → infected with antigen, won’t kill
cell because it is an APC cell and already engulfing antigens (acting as an
immune cell / doing its job)
→ Humoral Immunity
● Antigenic
determinants:
specific regions the
antibodies bind to
○ Body has to
make antibodies for each of these antigenic determinants to be able to tag cell
for destruction
○ Antibody only tags for destruction, doesn’t destroy it
,T vs B lymphocytes → work differently
- Infected with antigen,body makes antibodies
- B cells make antibodies (upregulate/ clone themselves)
- If this is the first time seeing the antigen it’s called the primary response (72
hours - 3 days)
Clonal selection - steps
1. B cells clone themselves upon encountering an antigen (1st degree response, 3-6 days)
2. Resulting plasma cells secrete antibodies into plasma ( 2000 every second)
a. “Antibody producing factories” - release antibodies into plasma aka humoral
immunity
3. Clone cells not differentiating into plasma cells become memory cells
a. Memory cells can stay with you for 20-30 years
b. Knows what antigen looks like
4. Re-infection produces a 2nd degree response
a. More antibodies are made secondary response (see below)
→ B-Cell Cloning
→ Humoral Response :
# of antibodies made
, - IgM (1) /IgG (2)= types of antibodies
*First exposure: day ⅔ (so nothing happens during this time)
*# of antibodies start increasing (primary exposure = small # of antibodies being made)
*# of antibodies starts to decrease after primary response
* day 28, re-exposed to same antigen, in ⅔ days # of antibodies skyrockets
→ Antibody Structure
● Antibodies your body makes are examples of: Immunoglobulins (Ig) [makes different
types: IgM, IgG]
○ 4 polypeptides / chains of amino
acids [2 Heavy, 2 Light]
○ What’s holding it together:
disulphide bonds (2 molecules of
sulfur)
○ Antibody monomer, T or Y shaped
- 2 antigen binding sites (recognize
antigenic determinant)
○ C (constant region)
■ Sequence of amino acids all
the same
○ V (variable region)
■ Sequence of amino acid
chains changes near the ends
■ This is because when the body is infected with different antigens V
regions try to attach to the antigen so they must make the ends specific to
those antigens
Image: Simplest type of antibody (monomer - looks like y or t)
● 4 polypeptide chains
○ Short chain = “light”
○ Long chain = “heavy”
→ Antibody Classes (the different types of immunoglobulins)
● Classification is based on C region in heavy chain
● IgD (1), IgG (2), IgE (3), IgA (4), IgM (5)
